https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98482
--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Uroš Bizjak from comment #2) > (In reply to Hongtao.liu from comment #1) > > and by the time of output __fentry__ in gcc, register is already accocated, > > is there any regs supposed to be safe in the entry of function? or we need > > to spill reg to stack and load it back after call, it looks inefficient. > > You can use any calee-saved register here. Eh, no - __fentry__ is called before pushes.
